全文获取类型
收费全文 | 1427篇 |
免费 | 71篇 |
国内免费 | 16篇 |
学科分类
工业技术 | 1514篇 |
出版年
2024年 | 3篇 |
2023年 | 30篇 |
2022年 | 67篇 |
2021年 | 89篇 |
2020年 | 65篇 |
2019年 | 87篇 |
2018年 | 123篇 |
2017年 | 88篇 |
2016年 | 81篇 |
2015年 | 50篇 |
2014年 | 75篇 |
2013年 | 162篇 |
2012年 | 89篇 |
2011年 | 98篇 |
2010年 | 64篇 |
2009年 | 72篇 |
2008年 | 36篇 |
2007年 | 25篇 |
2006年 | 24篇 |
2005年 | 19篇 |
2004年 | 13篇 |
2003年 | 16篇 |
2002年 | 12篇 |
2001年 | 10篇 |
2000年 | 3篇 |
1999年 | 6篇 |
1998年 | 12篇 |
1997年 | 5篇 |
1996年 | 2篇 |
1995年 | 12篇 |
1994年 | 3篇 |
1993年 | 5篇 |
1992年 | 8篇 |
1991年 | 9篇 |
1990年 | 4篇 |
1989年 | 2篇 |
1988年 | 4篇 |
1987年 | 3篇 |
1986年 | 2篇 |
1985年 | 6篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1981年 | 4篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1976年 | 5篇 |
1975年 | 4篇 |
1974年 | 6篇 |
1973年 | 2篇 |
排序方式: 共有1514条查询结果,搜索用时 0 毫秒
101.
Mohamed Fawzy Ramadan Mohamed Mostafa Afify Amer Ahmed El-Said Awad 《European Food Research and Technology》2008,227(4):1173-1182
Coriander (Coriandrum sativum L.) seed oil (COR) is a promising oil with high levels of bioactive compounds. Very little information, however, is available
on the effect of administration of COR on different aspects of plasma lipid profile in experimental animals. In view of the
important implications, the effect of administration of COR and oil blend [a mixture of soybean oil, coriander oil and sunflower
oil (4:2:4, w/w/w; Blend)] on the profile of plasma lipids was investigated in 24 male albino rats placed on a cholesterol-rich
(1%) basal diet as compared to rats on a cholesterol-free basal diet. Coriander seed oil and Blend were analyzed for composition
of fatty acid, sterol and tocopherol. The levels of bioactive compounds (sterols and tocopherols) were higher in COR than
in the Blend. In addition, the antiradical potential of COR and Blend was measured and the results showed that COR had stronger
radical scavenging activity than Blend. In the biological experiment, rats were divided into four diet groups. The negative
control group (control) consumed the basal diet (BD) only, which contained wheat starch, casein and cellulose, as well as
mineral and vitamin mixtures. To the BD were added 1 g/100 g cholesterol (Chol/group), or both (Chol/COR group) and (Chol/Blend
group). The groups did not differ before the experiment, which lasted 60 days. Plasma total lipids (TL), triacylglycerols
(TAG), total cholesterol (TC), low-density lipoprotein-cholesterol (LDL-C) and high-density lipoprotein-cholesterol (HDL-C) were measured at day 15, 30, 45 and 60 during the experiment period. Generally, COR and Blend-supplemented diets decreased
the levels of TL, TC, TAG and LDL-C in plasma. In addition, significant increase in the levels of HDL-C was observed for Chol/COR
and Chol/Blend groups. The results demonstrated that COR, and to a relatively lesser degree Blend, have hypocholesterolemic
properties in rats fed a cholesterol-rich diet. 相似文献
102.
Alaa El-Din Abdin Mostafa A. M. Abdeen 《Journal of Mechanical Science and Technology》2005,19(8):1582-1596
Groundwater flow and behavior have to be investigated based on heterogeneous subsurface formation since the homogeneity assumption
of this formation is not valid. Over the past twenty years, stochastic approach and Monte Carlo technique have been utilized
very efficiently to understand the groundwater flow behavior. However, these techniques require lots of computational and
numerical efforts according to the various researchers’ comments. Therefore, utilizing new techniques with much less computational
efforts such as Artificial Neural Network (ANN) in the prediction of the stochastic behavior for the groundwater based on
heterogeneous subsurface formation is highly appreciated. The current paper introduces the ANN technique to investigate and
predict the stochastic behavior of a well draw down in a confined aquifer based on subsurface heterogeneous hydraulic conductivity.
Several ANN models are developed in this research to predict the unsteady two dimensional well draw down and its stochastic
characteristics in a confined aquifer. The results of this study showed that ANN method with less computational efforts was
very efficiently capable of simulating and predicting the stochastic behavior of the well draw down resulted from the continuous
constant pumping in the middle of a confined aquifer with subsurface heterogeneous hydraulic conductivity. 相似文献
103.
Mostafa A. M. Abdeen 《Journal of Mechanical Science and Technology》2008,22(9):1830-1842
Most of the open water irrigation channels in Egypt suffer from the infestation of aquatic weeds, especially the submerged
ones that cause numerous hydraulic problems for the open channels themselves and their water distributaries such as increasing
water losses, obstructing water flow, and reducing channels’ water distribution efficiencies. Accurate simulation and prediction
of flow behavior in such channels is very essential for water distribution decision makers. Artificial neural networks (ANN)
have proven to be very successful in the simulation of several physical phenomena, in general, and in the water research field
in particular. Therefore, the current study aims towards introducing the utilization of ANN in simulating the impact of vegetation
in main open channel, which supplies water to different distributaries, on the water surface profile in this main channel.
Specifically, the study, presented in the current paper utilizes ANN technique for the development of various models to simulate
the impact of different submerged weeds’densities, different flow discharges, and different distributaries operation scheduling
on the water surface profile in an experimental main open channel that supplies water to different distributaries. In the
investigated experiment, the submerged weeds were simulated as branched flexible elements. The investigated experiment was
considered as an example for implementing the same methodology and technique in a real open channel system. The results showed
that the ANN technique is very successful in simulating the flow behavior of the pre-mentioned open channel experiment with
the existence of the submerged weeds. In addition, the developed ANN models were capable of predicting the open channel flow
behavior in all the submerged weeds’cases that were considered in the ANN development process 相似文献
104.
The grafting of methyl methacrylate (MMA) onto ultra‐high‐molecular‐weight polyethylene (UHMWPE) and chromic acid etched UHMWPE was conducted with a preirradiation method in air in the presence of a Mohr salt and sulfuric acid. The grafted samples were characterized by Fourier transform infrared (FTIR) spectroscopy, a gravimetric method, differential scanning calorimetry, scanning electron microscopy (SEM), and interfacial bonding strength measurements. The FTIR results showed the presence of ether and carbonyl groups in the MMA‐grafted UHMWPE (MMA‐g‐UHMWPE) samples. The Taguchi experimental design method was used to find the best degree of grafting (DG) and bonding strength. The efficient levels for different variables were calculated with an analysis of variance of the results. SEM micrographs of MMA‐g‐UHMWPE samples showed that with increasing DG and chromic acid etching, the MMA‐g‐UHMWPE rich phase increased on the surface; this confirmed the high interfacial bonding strength of the grafted samples with bone cement. The grafting of the MMA units onto UHMWPE resulted in a lower crystallinity, and the crystallization process proceeded at a higher rate for the MMA‐g‐UHMWPE samples compared to the initial UHMWPE; this suggested that the MMA grafted units acted as nucleating agents for the crystallization of UHMWPE. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 相似文献
105.
A series of novel aromatic poly(ester‐ether‐imide)s with inherent viscosity values of 0.44–0.74 dL g?1 were prepared by the diphenylchlorophosphate‐activated direct polycondensation of an imide ring‐containing diacid namely 5‐(4‐trimellitimidophenoxy)‐1‐trimellitimido naphthalene ( 1 ) with various aromatic dihydroxy compounds in the presence of pyridine and lithium chloride. Owing to comparison of the characterization data, an ester‐containing model compound ( 2 ) was also synthesized by the reaction of 1 with phenol. The model compound 2 and the resulted polymers were fully characterized by FT‐IR and NMR spectroscopy. The ultraviolet λmax values of the poly(ester‐ether‐imide)s were also determined. The resulting polymers exhibited an excellent organosolubility in a variety of high polar solvents such as N,N‐dimethylacetamide, N,N‐dimethylformamide, dimethyl sulfoxide, and N‐methyl‐2‐pyrrolidone. They were soluble even in common less polar organic solvents such as pyridine, m‐cresol, and tetrahydrofuran on heating. Crystallinity of the polymers was estimated by means of wide‐angle X‐ray diffraction. The resulted polymers exhibited nearly an amorphous nature. From differential scanning calorimetry thermograms, the polymers showed glass‐transition temperatures between 221 and 245°C. Thermal behaviors of the obtained polymers were characterized by thermogravimetric analysis, and the 10% weight loss temperatures of the poly(ester‐ether‐imide)s were found to be over 410°C in nitrogen. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 相似文献
106.
Two-dimensional particle image velocimetry (PIV) is usually used to determine the complex flow field in mechanically agitated vessels on the basis of measurements taken in a single vertical plane, thus, assuming axial symmetry. In this paper, we use 2D PIV to investigate the effects of the azimuthal position of the measurement plane in a fully baffled vessel agitated by a pitched blade turbine. Seventeen planes located at 5 degree intervals between two adjacent baffles are analysed. To maintain a high spatial resolution of ~1 mm when examining each plane, a two-block approach is employed combining data from two fields of view to reconstruct the whole flow field. Time-averaged velocity and turbulent kinetic energy fields are obtained under fully turbulent conditions as a function of the azimuthal position of the laser plane. It is shown that the assumption of axial symmetry for such Eulerian fields is not fully justified within a fully baffled vessel, as there are considerable differences between planes. The results also show for the type and size of impeller used here, the importance of including both the axial and radial discharge contributions for an accurate evaluation of the flow number, otherwise it can be underestimated by up to 60%. The three-dimensional nature of the PIV measurements has also enabled the mass continuity to be accurately verified throughout the vessel. 相似文献
107.
If 100 dice cannot be cast simultaneously, one single die can be cast 100 times. On the basis of this simple principle, the experimental technique of positron emission particle tracking has been used to develop and implement a new methodology for quantifying the local and global mixing characteristics within a mechanically agitated fluid batch system. This Lagrangian technique uses a single positron-emitting particle as flow follower. Using a high data acquisition rate, such a tracer is continuously tracked in 3D space and time to accurately determine its trajectory over a considerable period of time. By partitioning its long trajectory, the single particle tracer can be regarded as thousands of simultaneously tracked particles which are instantaneously, locally and non-invasively injected in the mixing system at varying feed positions. A large amount of PEPT data were collected for impeller rotational speeds ranging from 100 to 500 rpm which allowed new statistical tools derived from information theory, such as Shannon entropy and uncertainty, to be implemented in the data analysis. Thus, measurements of entropy mixing indices were obtained as a function of position, time and impeller speed. The method also allowed the determination of characteristic time parameters including the macroscale mixing time which agreed very well with correlations of the dimensionless mixing time available in the mixing literature. Detailed local information is provided on minimum mixing time positions for feed and withdrawal of material, which can be used to optimise the design or operation of stirred batch mixing systems. 相似文献
108.
Muhammad Mostafa Monowar Muhammad Mahbub Alam Md. Obaidur Rahman Choong Seon Hong Sungwon Lee 《电信纪事》2010,65(11-12):777-794
Being a pivotal resource, conservation of energy has been considered as the most striking issue in the wireless sensor network research. Several works have been performed in the last years to devise duty cycle based MAC protocols which optimize energy conservation emphasizing low traffic load scenario. In contrast, considering the high traffic situation, another research trend has been continuing to optimize both energy efficiency and channel utilization employing rate and congestion control at the MAC layer. In this paper, we propose A Load-aware Energy-efficient and Throughput-maximized Asynchronous Duty Cycle MAC (LET-MAC) protocol for wireless sensor networks to provide an integrated solution at the MAC layer considering both the low-and high-traffic scenario. Through extensive simulation using ns-2, we have evaluated the performance of LET-MAC. LET-MAC achieves significant energy conservation during low traffic load (i.e., no event), compared to the prior asynchronous protocol, RI-MAC, as well as attains optimal throughput through maximizing the channel utilization and maintains lower delay in regard to the CSMA/CA-like protocol during a high volume of traffic (i.e., when an event occurs). 相似文献
109.
Mohammad Aberoumand Kianoosh Soltanmohammadi Davood Rahmatabadi Elyas Soleyman Ismaeil Ghasemi Majid Baniassadi Karen Abrinia Mahdi Bodaghi Mostafa Baghani 《大分子材料与工程》2023,308(7):2200677
In this research, polyvinyl chloride (PVC) with excellent shape-memory effects is 4D printed via fused deposition modeling (FDM) technology. An experimental procedure for successful 3D printing of lab-made filament from PVC granules is introduced. Macro- and microstructural features of 3D printed PVC are investigated by means of wide-angle X-ray scattering (WAXS), differential scanning calorimetry (DSC), and dynamic mechanical thermal analysis (DMTA) techniques. A promising shape-memory feature of PVC is hypothesized from the presence of small close imperfect thermodynamically stable crystallites as physical crosslinks, which are further reinforced by mesomorphs and possibly molecular entanglement. A detailed analysis of shape fixity and shape recovery performance of 3D printed PVC is carried out considering three programming scenarios of cold (Tg −45 °C), warm (Tg −15 °C), and hot (Tg +15 °C) and two load holding times of 0 s, and 600 s under three-point bending and compression modes. Extensive insightful discussions are presented, and in conclusion, shape-memory effects are promising,ranging from 83.24% to 100%. Due to the absence of similar results in the specialized literature, this paper is likely to fill a gap in the state-of-the-art shape-memory materials library for 4D printing, and provide pertinent results that are instrumental in the 3D printing of shape-memory PVC-based structures. 相似文献
110.
Mohamed Mostafa Saied 《电力部件与系统》2014,42(11):1143-1151
Abstract—This article proposes a new approach to study the frequency response and the transient analysis of power transformer windings. For improved accuracy, the suggested model includes, among other equivalent circuit elements, the mutual magnetic couplings between any winding turn and all others. This implies that the equivalent inductance of any considered turn will be a location-dependent parameter. Accordingly, the winding will be analyzed as a non-uniform transmission line. Through the application of a recursive circuit reduction technique, a closed-form Laplace s-domain analytical expression for the winding's input impedance can be obtained for any neutral treatment. The resulting expression can be used to determine the winding's series and parallel resonance frequencies. The s-domain expression for the input impedance, in connection with the numerical inverse Laplace transform, will be utilized for determination of the winding's time-domain transient response for any input voltage or current time waveform. Accuracy increases with the assumed number of winding sections, which can be even increased to the actual number of turns, limited only by the available computation resources. The results of case studies are in good agreement with those available in the literature using the time-domain solution of the simultaneous differential equations in the state variables. 相似文献